Curvature
by trollnexus
Summary: Cassiopeia despised the number three.


**Title**: Curvature

**Disclaimer**: JKR's universe is all hers, and I earned no money from the writing of this fic.

**Pairings**: Cassiopeia Black/Horace Slughorn (whether one-sided or not is up to your imagination)

**Rating**: T

**Warnings**: A mention of Christianity-bashing from a pureblood wizard's viewpoint. Infidelity. Numbers obsession.

**Summary**: Cassiopeia despised the number three.

**Word Count**: 3,239

**Prompts**: Sentence: The clock on the wall seems to be ticking backwards.

Happy families are all alike; every unhappy family is unhappy in its own way. – Leo Tolstoy, Anna Karenina (One of my favourite novels, by the way.)

And she was the first beautiful thing I ever got stuck on. – Neil Hilborn, OCD (Gender reversed, though.)

**Author's Note**: This is my entry for Round 8 of the Quidditch League Fanfiction Competition.

No one is sure when exactly Slughorn started teaching at Hogwarts, so I tweaked the timeline to suit my needs.

I only use the first prompt verbatim; the other two are implied.

And that's it; no preachy message for today, for I am way too sleep-deprived for this.

* * *

The clock on the wall seemed to be ticking backwards.

_Tock-tick, tock-tick, tock-tick._

It grated on her nerves, and she struggled to hear it correctly again, to connect the ticks to the tocks in their proper order, but then the tock-tick assaulted her ears again.

Worse, she was hearing it in threes instead of her preferred fives, and three was the worst. Nothing good came in threes.

Case in point: Father, Mother, and Father's mistress.

Cassiopeia stabbed her parchment with her quill, wanting to stab the thought, too. What was the point in moping? Slytherins do not mope.

Slytherins plot revenge.

But not now. Now was the time for class. She needed to earn top marks for the sake of her family, Father be damned.

She sighed and scribbled, wishing Binns could be just a bit less boring for once, but also resigning herself to the fact that sometimes one had to accept what one had.

Fortunately, in other areas of her life, she had a lot. Disgraceful fathers aside, being a Black was invaluable.

Or at least, that was what she told herself.

* * *

Cassie quietly endured the nattering of her fellow Slytherins at the lunch table, occasionally offering a polite smile as a sop to those pathetic bloodhounds. They valued pure blood and always chased after her because of it, but they didn't really understand the full value of her blood. All they knew was that being on her "good side" somehow led to "good things."

She itched to sneer at them, but a proper lady never sneered in public, so she crossed her legs and let her rigid posture remind them of their place instead.

Honestly, she was lonely. Pollux had graduated long ago, Marius had turned out to be a Squib, and Dorea was too young to provide her with any stimulating conversation.

She spared a glance for Dorea anyway, but her little sister was, as always, picking disinterestedly at her plate.

_Scrape, scrape, scrape, scrape_, went Dorea's fork. Counts of four. Probably not intentional, since she occasionally broke the rhythm, but there all the same.

When no one was looking, Cassie wordlessly levitated a pea and flung it at her in order to end the imperfect beat.

Dorea flinched as the pea hit the exact centre of her forehead and looked up, glaring with fork still in hand.

Cassie smiled angelically, and although a nearby boy seemed to swoon at the sight, Dorea scowled even more.

"Do try to smile more often, dearest Dorie," crooned Cassie. "Remember what Mother taught us."

Dorea grimaced, which was her best approximation of a smile, and Cassie shrugged, turning away. The child would learn respect eventually. Cassie did not have the time or patience to nag her about her manners.

She cast _Tempus_, which conjured her favourite, tockless clock, letting out an airy sigh as she pretended to see the time.

"Please excuse me, my dears, but I must head to Potions."

"But it doesn't start for yet another hour," fawned a fifth year whose name escaped her. "You're so dedicated to your studies, Cassiopeia!"

She patted him on the head, effectively silencing him.

"Of course. Only a fool would expect any less from me."

* * *

She made her way to the classroom, measuring out her footsteps as she went. She had to end on a multiple of five. On good days, she got it correct, but even on bad days, she would only have at most four steps left over.

When this happened, she simply stood in the doorway and gently scraped her shoes against the ground for the remaining steps, and it looked as if she were merely ensuring her shoes were clean before entering sacred ground. This ritual was part of the reason why she always headed for Potions early, for she did not want others to witness it.

Today she had two steps left over. Four, five.

Inside the classroom, an ornate chair watched her, and she rolled her eyes as she stepped inside. She ran her fingers against the smooth mahogany, tracing the delicate curvature. The seat was cushioned with what looked like soft material, but she did not dare press her hand against it or, worse, _sit_ on it. After all, that was a bit _too _much intimacy.

"Professor," she drawled to the chair. "You know you fool no one."

She quickly stepped back as the chair transformed into a man in his thirties, tall and of average build—with the exception of a growing belly, of course.

"Miss Black!" boomed Horace as he wagged his finger at her, his eyes twinkling. "I can never get anything past you, can I?"

"I have had years of practice, sir."

It was true. Professor Slughorn had been teaching at Hogwarts since Cassie was a first year, and he tried to play the same chair trick on her almost every day. Occasionally he would bring in an actual chair in an attempt to throw her off, but she recognised him through a certain feel.

She would have said she sensed his soul if she really believed in one, but instead she conjectured that she felt his magic. It was a reasonable hypothesis, since Slughorn, for all his joviality, was quite powerful. Not as powerful as Dumbledore or Grindelwald, of course, but definitely someone worth feeling, more than her pathetic schoolmates.

That was the problem, she thought to herself as she watched him prepare his materials for today's lesson. Despite her best efforts, she had developed a ridiculous infatuation for this silly chair-man with a belly and a penchant for gifts from teacher's pets. It was inconvenient, especially as she knew he could never and would never return her feelings. If she had the same self-control as her mother, she would have smothered those feelings already and sought someone she _could_ marry.

Then again, what was the point of self-control when it trapped you into a state of inaction as your husband sneaked off to another woman?

She swallowed the bile that filled her mouth at the thought. Damn, why couldn't she just let the thought _go_? So her father had turned out to be a disgusting pig. Worse things had happened. Marius happened, hadn't he?

She cringed as she felt her thoughts spiral down that pathway. No, it was best to turn her attention back to Horace and admire his well-polished buttons. (There were five of them, and this pleased her immensely.) Yes, it was an unhealthy obsession, but it was better to focus on him than to focus on the uglier parts of her life.

As she fixated on the sheen of his buttons, she began to calm down, her breathing settling into a steady rhythm. She was here with the man she admired, and she was going to do some precision work with all the right ingredients and supplies. That was all that mattered here: Horace and potions.

* * *

Potions class had left her in such a good mood that she permitted Dorea to sit next to her at dinner. Dorea eyed her askance but said nothing, taking more care to eat her food properly rather than scraping her fork against the plate. Cassie rewarded her with an indulgent smile, and Dorea frowned, concentrating even harder on her meal.

"The two of you look so good together," commented one of Cassie's many admirers, his eyes roaming covetously over the two of them.

Cassie allowed the corners of her mouth to tilt down just the slightest bit, and he flushed, turning to face his plate. She made note to watch him more closely in the future. Dorie may only be twelve at the moment, but some men had baser desires than others.

"Cassiopeia," murmured Dorea, cutting off Cassie's bitter string of thought. "May I be excused? I do not feel well."

Cassie examined her face, looking for traces of illness, and noted that her forehead _did_ look a bit sweaty. She touched her forehead, which was quite warm, confirming her suspicions.

"Very well. I will take you to bed. I have lost my appetite, anyway." Her eyes flicked towards the rude boy again, and he cringed as if she had whipped him. Good.

Satisfied that he would not follow them, she led Dorea out of the Great Hall, holding her little hand.

* * *

The moment they reached the dungeons, however, Dorea began walking faster, pulling Cassie along. Cassie opened her mouth to complain that older sisters were _not_ supposed to be yanked like a Crup on a leash, but she found herself in Dorie's room before she could utter a word.

As the door shut behind them, Cassie rounded on her. "What is the matter with you?" She pressed her hand on Dorie's forehead again and found it cool to the touch. "You _faked_ your illness!" she hissed, although part of her was proud of Dorea for succeeding in fooling her. She wondered what potion or spell she had used.

"My apologies, Cassiopeia, but I _had_ to. It is impossible to request an appointment with you, what with your potions obsession and your sickening sycophants."

Cassie smirked. "Jealous? If you missed me, you should have said so."

Dorea shook her head. "I was instructed to get you alone."

Cassie tensed, feeling the air tighten around them. "'Instructed'?"

Dorea reached into her pocket and held out, her fingers slightly trembling, a sealed envelope.

Cassie's fingers did not tremble at all as she accepted the letter, but only because she was counting slowly in her head. Was this a letter from Father? Had he discovered that she had espied his infidelity?

Upon closer examination of the seal, however, she concluded it was from Pollux. As he was not yet head of the House, his seal was slightly smaller and less imposing, although the beautiful script-_B_ was still visible.

"What does he want?" she muttered, and Dorea shrugged. Of course she would not know; there had probably been a letter warning Dorea that her fingers would fall off if she opened what was not hers. Such threats from Pollux were common but by no means idle.

With that in mind, Cassie carefully and gently broke the seal, and a puff of magic kissed her fingers, acknowledging her as the rightful recipient. She rolled her eyes, because she was alone with Dorea and she could. Pollux wasted his magic on such silly gestures.

The letter, however, was not silly at all.

There were no words; the entire parchment was dedicated to a detailed ink rendering of a beautiful woman draped in a blue cloth, serenely standing on top of a serpent, letting the weight of her purity bear down and crush the evilness of the world.

Father had sneered at the image when they first saw it embedded in the window of a Muggle church, saying that Muggles were fools to think snakes were evil, that they hated pure wizards like them and wanted to stamp them out. He then spat on the glass, hitting the woman's dress, declaring that she was the emblem of arrogant Mudbloods who thought _they_ had the right to decide what was evil.

Pollux had been eight years old at the time, and he caught five-year-old Cassie's eyes and smirked. Unbeknownst to their father, they had interpreted the image differently.

Even as their father took out his wand and set the church on fire, Pollux had held her hand and whispered that the woman did not have to be the Muggle representative if they did not want her to be. The woman could be _theirs_ if they found the right snake.

Now, all these years later, the message was clear: Pollux had finally discovered the serpent in their family, and judging from the fact that this rendition of the woman looked remarkably like Cassie, he wanted _her_ to be the one to crush the serpent under her feet.

Cassie swallowed and looked over at Dorea, who was watching in silence.

Any other little sister would have immediately clamoured for an explanation or at least tried to peek at the letter.

Dorea, however, was not the little sister in just any old family. All happy, "normal" families were painfully predictable, but their family would always shift and change in accordance with their situation, and Dorea was exhibiting that trait right now with the way her eyes tracked Cassie's every motion, her wand never too far from her hand.

Cassie knew that if she let the wrong emotion flicker on her face, Dorea would stun or bind her in the next moment. Pollux's presence, bodily or otherwise, always had that effect on them, because he knew how to pull their wires taut.

Cassie forced herself to release a careless snort and fold the parchment clumsily, even though her fingers itched to make every fold smooth and precise. Let Dorea think that she felt contemptuous and annoyed rather than terrified.

"All that fuss over nothing, Dorie. He just wants to nag me about the husband issue."

Dorea's body uncoiled. "Ridiculous. Your debut is next summer; what is the point of nagging you now?"

Cassie patted her head before moving towards the doorway. "He fancies himself to be our father figure, the fool."

Dorea's startled chuckle was Cassie's only consolation as she went off to fulfil her duty.

* * *

She had expected breaking into Horace's supplies room to be difficult. The damnable man seemed to covet every single one of his possessions even as he chased after the acquisition of more. Yet the door opened with a simple _Alohomora_, and she concluded that Horace severely underestimated his students.

What a shame, that, but Cassie was not here to meditate on Horace's flaws. She wanted to gather hellebore and moonstone, among other things. It depended on what she could find here. She knew she wanted to brew an effective poison, but she did not know what supplies would be available, even in Horace's private stores.

Just as her fingers closed around a moonstone, however, she felt fingers close around her wrist.

"How disappointing, Miss Black. I expected better of you."

She inhaled and exhaled slowly, refusing to show fear or resentment at having been caught. "Hello, Professor Slughorn."

His fingers moved slightly, almost caressing her wrist, but she could not enjoy that right now, not when he had the potential to ruin her and her family.

As if he were discussing the matter over tea, he commented, "Did you know, Miss Black, that I find it more amusing to catch thieves in the act than to prevent theft completely?" With his other hand, he effortlessly pried the stone out of her fingers and dropped it back into the box.

"I care not for your taste in entertainment, sir. That is beyond the scope of our teacher-student relationship."

He sighed, but it was an airy sigh, and she half-expected the sigh to become a poetic sprite and start sermonising on the merits of not touching Horace's bloody supplies.

"My child, if you were in your right mind, you would not lie to me, and in fact you would not be here at all. You would be in your dorm, resting in your comfortable bed!" Here he chortled a bit, and she had never found him more unattractive. "But alas! You are here in this private appointment with me. What an honour for you, is it not?"

She pulled on her hand, but he held fast. For a man that was getting progressively pudgier, he had fingers like manacles.

"It is indeed an honour, sir, but now that you mention it, I really do need to rest my mind for your class."

His next chuckle sent a chill down her spine. "That may be so, but we need to have a chat about the _reason_ you have elected to bestow this honour upon yourself tonight. Tell me, Cassiopeia, why would you need a moonstone? I do not recall assigning the Draught of Living Death to your class this year, and any other reason for using it cannot be very…pleasant."

"I am not obligated to answer that question, sir."

"Mm, indeed you are not. Even if I were to punish you, there would be no incentive for you to reveal your motivations. Fair enough. But I can guess easily. You want to seek revenge against your father, don't you?"

She pulled her hand again, and still he held fast. She contemplated hexing him, but she heard rumours that Horace was a skilled duellist, despite his unintimidating looks. There was no point in risking death, not even for revenge.

"Do not be surprised, Miss Black. I have more than enough connections to be aware of your familial woes."

She wanted to hiss, maybe even howl. Father was definitely not as discreet as he should have been.

Horace continued, "Although I understand you feel betrayed on behalf of your family's honour, patricide is heavily frowned upon, especially when it is committed by someone who is not the heir apparent."

She really did hiss then. Didn't he _understand_? Pollux could never defeat Father in a duel, and if he tried to kill him some other way, he would lose his right to be heir, sending the family into chaos. If _Cassie_ were the one to kill him, though, she would lose _nothing_—

"You still have your soul to lose, child, and I will not let you lose it with _my_ supplies."

"What does it matter? I am just a daughter, and I am probably never going to find a suitable husband anyway, so I will not continue the line."

"You have a responsibility, Miss Black. What would happen to Dorea if both her father and sister were gone?"

Unbidden, she thought of the lecherous Slytherin boy again and the dangers he represented to her fragile, still-naïve sister. Dorea had more to learn, and Mother would be no help if she became a widow. Horace was right; Cassie had more to lose than just her soul.

Yet there was still the issue of Pollux.

"I cannot defy the wishes of my elder brother, sir."

Horace pulled her towards the door, perhaps sensing her hesitation and capitalising on it. "You were ready to defy your father by taking away his _life_. Surely your brother presents a smaller threat. Besides."

They had reached the doorway, and he had planted her body firmly outside it. He leaned in.

"I will take care of Pollux. I daresay I know something about him that might give him pause."

She looked up at him and saw, for the first time, a hard glint in his eyes. "What's in it for you, sir?"

His eyes locked with hers, and they stood in silence with his hands on her shoulders.

Then he shrugged, letting go. "I am not obligated to answer that question. Now go back to your dorm before I have to come up with an appropriate punishment for breaking into my storeroom."

There was no point in arguing, so she turned away.

As she walked, she counted the steps that she took back towards her room. The 205th step took her to her bed, so she knew that listening to his advice had been the right decision.

Maybe one day she would come up with a better revenge, one that would not put the rest of the family in jeopardy.

But for now, she took her foot off the serpent and let it live another day.


End file.
